Ultra wideband (UWB) wireless communication has been the subject of significant research interest in recent years. In a traditional single-band UWB system, a series of pulses with very short duration, typically on the order of a nanosecond (ns) or less, is transmitted to convey data. UWB therefore holds great promise for high data rate wireless applications. However, because of the extremely short pulse width, the spectrum of a UWB signal often spans several Gigahertz (GHz), which can overlay bands of existing narrowband systems.
To be accepted for widespread applications with negligible interference to existing narrowband systems, UWB devices are required to meet a strict power spectrum density (PSD) constraint that is set by the Federal Communication Commission (FCC). Consequently, single-band UWB systems have some drawbacks. For example, it has been inefficient to utilize the whole UWB spectrum (e.g., 3.1 GHz to 10.6 GHz) while also meeting the FCC PSD constraints. In other words, conventional approaches do not enable full UWB spectrum use while concomitantly avoiding interference from and/or to narrowband systems (e.g., such as those operating in accordance with IEEE 802.11a).
In response to this deficiency of conventional approaches, a multi-band UWB system has been proposed. Specifically, a multi-band UWB system has been proposed in conjunction with IEEE 802.15.3a in a standards meeting therefor. In such a system, in contrast to the single-band UWB system, the whole UWB band is divided into multiple disjoint sub-bands. Each of the sub-bands occupies fractional bandwidth of the total UWB spectrum (3.1 GHz to 10.6 GHz). A carrier with a different centre frequency in each sub-band is modulated by a somewhat wider pulse (e.g., a pulse having a width of approximately 3 ns) during transmission.
Due to the strict FCC PSD constraints, UWB systems are power limited systems regardless of whether they are operated as single-band or multi-band systems. To reduce the impact of the power limitation on system range and/or data throughput, a power efficient UWB modulation scheme may be employed. Several modulation schemes for UWB systems have been proposed. These proposed schemes include: Pulse Amplitude Modulation (PAM) schemes and Pulse Position Modulation (PPM) schemes. PAM schemes include Binary Phase Shift Keying (BPSK) and On-Off Keying (OOK) modulation schemes. PPM schemes include an M-ary Equicorrelated (EC) PPM scheme, an M-ary PPM scheme using Walsh Codes, and an M-ary orthogonal PPM scheme. None of these proposed schemes, however, fully utilize the spectrum allocated to UWB systems while avoiding interference with narrowband systems.
Accordingly, there is a need for schemes and/or techniques that can modulate wireless communications in UWB systems in a power efficient manner.